Prior work from our laboratory has shown that iodine deficiency produced by dietary restriction causes specific tissue changes in rat breasts especially in the presence of sex steroids - estrogen or testosterone. These dysplastic reactions differ histologically and metabolically from those seen in induced hypothyroid states. We have confirmed the presence of iodine in the breast and have demonstrated further that the breast changes seen to vary with the quantity of iodine present and the generalized iodine status of the rat. A pilot study using an anion blocking agent, perchlorate, showed changes in breast duct epithelium. The proposed research will further correlate breast histology with breast iodine uptake using perchlorate. Breast changes will be studied in eu-, hyper-, and hypo-thyroid states and under the influence of sex steroid hormones and cortisone with iodine blockade. In addition, our preliminary studies have shown cytoplasmic estrogen receptor protein (ERP) increases in breasts of iodine deficient rats as compared with normals. ERP determinations will be expanded to include our projected experimental conditions. This research project is directed towards our overall research objective of determining the effects of iodine metabolism in the production of breast dysplasia and neoplasia.